Look if ULN2803 to see if it fits your needs.
If you connect the NPN to 9V as Paul__B suggested, you will still have plenty of volts left, so no problem even with blue/white displays. But don't forget to recalculate your series resistors for 9V rather than 5V!
So I've used MOSFET's before but it looks like basic BJT transistors are a lot cheaper. So I would like to figure out how to select one of them. My basic project is a 4 digit 7 segment display, common anode. So each of the 4 digits get's it's own supply and all the individual segments get grounded, through a 220ohm resistor, to turn on. I checked with my DMM and each of the single digits can pull close to 60mA. Since I'll be multiplexing they'll need to turn on and off at least 50 times a second. So where do I go from here in selecting a transistor? What other information do I need to do this? I'm thinking I'll be using a 9V battery to power this project with a 5V regulator. So the transistor will probably switch the same amount of current it will be feeding,+5V.
Quote from: PaulRB on Aug 19, 2014, 09:37 amIf you connect the NPN to 9V as Paul__B suggested, you will still have plenty of volts left, so no problem even with blue/white displays. But don't forget to recalculate your series resistors for 9V rather than 5V!May I suggest you re-think your advice here?
The point is that on a 5V supply, presuming the chip output will pull up to nearly 5V, the emitter can be pulled up to nearly 4.3V - less actually as the chip output - when driving current - can not pull up to nearly 5V. Since it is in fact, an emitter follower, it makes almost no difference whether the collector is supplied from 5V or 9V.
Schematics ALLWAYS says more than 1000 words